The present invention, in some embodiments thereof, relates to a polymeric device, and more particularly, but not exclusively, to a polymeric device useful for the treatment of an aneurysm and to polymeric systems useful for forming such a device.
The formation of aneurysms is a life-threatening degenerative pathology of arterial tissues whereby the wall of the artery weakens locally and markedly expands, creating a sac, which can potentially rupture. The expanded arterial sections are considered aneurysms of clinical relevance when their diameter is at least twice that of the normal artery. Before rupture occurs, an aneurysm seldom causes symptmatic pain or other symptoms. The bulging of the artery and its rupture typically occur in specific locations in the brain and in the thoracic and abdominal aorta. Abdominal aortic aneurysms (AAA) are particularly deadly, with fewer than 20% of victims surviving AAA rupture. Bursts of abdominal aortic aneurysms (AAA), the most common type of aneurysm, are ranked as the 13th most common cause of mortality in the U.S, and the 10th most common cause among U.S. men over the age of 55. Abdominal Aortic Aneurysms are present in about 1.2 million people in the U.S. (as of 2008).
The formation of an aneurysm is accompanied by a profound histological change in the tissue composition of the arterial wall. While the elastin and collagen content of a healthy aorta are about 36% and 23%, respectively, aneurysmal tissue displays a much lower elastin content (about 6%) and a much higher collagen content (about 45%). These changes result in a marked change of mechanical properties, with the longitudinal tensile strength decreasing from approximately 160 kPa to approximately 120 kPa, and the stiffness increasing from approximately 275 kPa to approximately 450 kPa.
Aneurysms are especially common in adult and elderly populations, particularly white men above the age of 55. According to current theories, an underlying genetic factor is likely involved in the formation of aneurysms, although additional factors such as high blood pressure, arteriosclerosis and smoking also play a role.
The mortality rate of aneurysms is high because the creation and expansion of aneurysms is a silent process until a burst occurs. The risk of rupture can be estimated by the size of the aneurysm. It is widely considered that the danger of rupture is high when the diameter of the aneurysm is about 5-6 centimeters, in which case the aneurysm should be treated without delay. In the case of smaller aneurysms, surgeons tend to differ as to the need for surgery.
Until 1991, the only available treatment entailed a fully open surgical procedure, whereby the dilated segment of the artery was replaced by an artificial vascular graft. The traditional treatment of AAA is performed by open abdominal surgery with full anesthesia, putting aside the abdominal organs, clamping the aorta and replacing the aneurysmal segment with Dacron® (polyethylene terephthalate) or expanded PTFE (polytetrafluoroethylene) arterial prostheses. These grafts have been widely implanted for several decades with good results, but have all the drawbacks associated with invasive surgical procedures. Intraoperative mortality rates range from approximately 2% to above 10%, and post-operative morbidity of 30% has been reported. In addition, even without complications, patients must remain in the hospital for 7 to 10 days after surgery, and are usually able to return to work only after about 6 weeks.
An endograft consisting of a vascular prosthesis mounted on a stent, and deployed intraluminally at the aneurysmal site using a balloon, was implanted for the first time in 1991. Once the stent is locked in place and the prosthesis is firmly positioned, the balloon is deflated and retrieved. This minimally invasive technique, named Endovascular Aortic Repair (EVAR), has several advantages, the most important of which stems from the much shorter hospitalization and recovery periods required by this technique. Patients undergoing EVAR are usually discharged after two days in the hospital and are fully recovered after approximately two weeks.
However, various factors restrict the use of EVAR. Consequently, only about 60% of AAA repair treatments are performed using the stent/graft system. Rather strict anatomical considerations pertaining to the dimensions of the artery both proximal and distal to the aneurysmal site may prevent the use of the graft. For example, if the diameter of the proximal vessel is too large, the device may dislodge from its intended position.
In addition, renewed leakage into the aneurysmal sac (endoleak) is a major problem. There are four types of endoleaks: migration or lack of sealing; leakage through arteries in branching points; leakage through the fabric; and leakage through other components of the stent/graft device. The different types of endoleaks can result in the burst of the aneurysm despite the presence of the graft, and approximately 50% of such ruptures lead to the death of the patient.
Furthermore, it was found that in approximately 40% of EVAR procedures, there was no change in the aneurysmal sac.
In addition, the stent/graft device used in EVAR is quite expensive, and may cost approximately 12,000 $.
U.S. Patent Application having Publication No. 2008/0063620 describes a polymeric system in which a polymeric component is capable of undergoing a transition that results in a sharp increase in viscosity in response to a change in temperature. The polymers are suitable for biomedical applications, such as drug delivery systems, prevention of post-surgical adhesions, sealants and tissue engineering.
U.S. Patent Application having Publication No. 2007/0116666 describes polyester/poly(oxyalkylene) triblock and diblock copolymers for reducing post-surgical adhesions.
U.S. Patent Application having Publication No. 2008/0133001 describes a medical device comprising a tubular structure for implantation in a vasculature, composed of a plastically deformable fiber. The plastically deformable fiber comprises a non-distensible polymer and an elastic polymer.
Additional background art includes U.S. Pat. No. 7,425,322; U.S. Pat. No. 7,569,643; International Patent Application PCT/IL2002/00699 (published as WO 2003/017972); International Patent Application PCT/IL2009/000865 (published as WO 2010/026590); and U.S. Patent Application having Publication No. 2010/0136084.